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Merge pull request #162 from 1999/tame-object-fields

Add support for fields from objects passed as function parameter
Fixes #157

Rather than using SourceNodeMock objects when source maps are
disabled, use raw strings for better performance.
Cleanup.

* rename toSourceNode() to toSourceNodeWhenNeeded()
* clean up loop variables in flattenString()
Merge pull request #164 from msridhar/improve-performance

Patch to address #157
Merge branch 'master' of https://github.com/Constellation/escodegen into vb-build